Cellphones and other devices could soon be controlled with touchless gestures and charge themselves using ambient light, thanks to new LED arrays that can both emit and detect light.
Made of tiny nanorods arrayed in a thin film, the LEDs could enable new interactive functions and multitasking devices. Researchers at the University of Illinois at Urbana-Champaign and Dow Electronic Materials in Marlborough, Massachusetts, report the advance in the Feb. 10 issue of the journal Science.
“These LEDs are the beginning of enabling displays to do something completely different, moving well beyond just displaying information to be much more interactive devices,” said Moonsub Shim, a professor of materials science and engineering at the U. of I. and the leader of the study. “That can become the basis for new and interesting designs for a lot of electronics.”
The tiny nanorods, each measuring less than 5 nanometers in diameter, are made of three types of semiconductor material. One type emits and absorbs visible light. The other two semiconductors control how charge flows through the first material. The combination is what allows the LEDs to emit, sense and respond to light.
The nanorod LEDs are able to perform both functions by quickly switching back and forth from emitting to detecting. They switch so fast that, to the human eye, the display appears to stay on continuously – in fact, it’s three orders of magnitude faster than standard display refresh rates. Yet the LEDs are also near-continuously detecting and absorbing light, and a display made of the LEDs can be programmed to respond to light signals in a number of ways.
For example, a display could automatically adjust brightness in response to ambient light conditions – on a pixel-by-pixel basis.
“You can imagine sitting outside with your tablet, reading. Your tablet will detect the brightness and adjust it for individual pixels,” Shim said. “Where there’s a shadow falling across the screen it will be dimmer, and where it’s in the sun it will be brighter, so you can maintain steady contrast.”
The researchers demonstrated pixels that automatically adjust brightness, as well as pixels that respond to an approaching finger, which could be integrated into interactive displays that respond to touchless gestures or recognize objects.
They also demonstrated arrays that respond to a laser stylus, which could be the basis of smart whiteboards, tablets or other surfaces for writing or drawing with light. And the researchers found that the LEDs not only respond to light, but can convert it to electricity as well.
“The way it responds to light is like a solar cell. So not only can we enhance interaction between users and devices or displays, now we can actually use the displays to harvest light,” Shim said. “So imagine your cellphone just sitting there collecting the ambient light and charging. That’s a possibility without having to integrate separate solar cells. We still have a lot of development to do before a display can be completely self-powered, but we think that we can boost the power-harvesting properties without compromising LED performance, so that a significant amount of the display’s power is coming from the array itself.”
In addition to interacting with users and their environment, nanorod LED displays can interact with each other as large parallel communication arrays. It would be slower than device-to-device technologies like Bluetooth, Shim said, but those technologies are serial – they can only send one bit at a time. Two LED arrays facing each other could communicate with as many bits as there are pixels in the screen.
“We primarily interface with our electronic devices through their displays, and a display’s appeal resides in the user’s experience of viewing and manipulating information,” said study coauthor Peter Trefonas, a corporate fellow in Electronic Materials at The Dow Chemical Company. “The bidirectional capability of these new LED materials could enable devices to respond intelligently to external stimuli in new ways. The potential for touchless gesture control alone is intriguing, and we’re only scratching the surface of what could be possible.”
The researchers did all their demonstrations with arrays of red LEDs. They are now working on methods to pattern three-color displays with red, blue and green pixels, as well as working on ways to boost the light-harvesting capabilities by adjusting the composition of the nanorods.
A land-grant university, it is the flagship campus of the University of Illinois system. The University of Illinois at Urbana–Champaign is the second oldest public university in the state (after Illinois State University), and is a founding member of the Big Ten Conference. It is a member of the Association of American Universities and is designated as a RU/VH Research University (very high research activities). The campus library system possesses the second-largest university library in the United States and the fifth-largest in the country overall.
The university comprises 17 colleges that offer more than 150 programs of study. Additionally, the university operates an extension that serves 2.7 million registrants per year around the state of Illinois and beyond. The campus holds 286 buildings on 1,468 acres (594 ha) in the twin cities of Champaign and Urbana; its annual operating budget in 2011 was over $1.7 billion.
University of Illinois at Urbana Champaign research articles from Innovation Toronto
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Bats have long captured the imaginations of scientists and engineers with their unrivaled agility, but their complex wing motions pose significant technological challenges for those seeking to recreate their flight in a robot.
The key flight mechanisms of bats now have been recreated with unprecedented fidelity in the Bat Bot—a self-contained robotic bat with soft, articulated wings, developed by researchers at Caltech and the University of Illinois at Urbana-Champaign (UIUC).
“This robot design will help us build safer and more efficient flying robots, and also give us more insight into the way bats fly,” says Soon-Jo Chung, associate professor of aerospace and Bren Scholar in the Division of Engineering and Applied Science at Caltech, and Jet Propulsion Laboratory research scientist. (Caltech manages JPL for NASA.)
Chung, who joined the Caltech faculty in August 2016, developed the robotic bat, along with his former postdoctoral associate Alireza Ramezani from UIUC and Seth Hutchinson, a professor of electrical and computer engineering at the UIUC and Ramezani’s co-advisor. Chung is the corresponding author of a paper describing the bat that was published on February 1 in Science Robotics, the newest member of the Science family of journals published by the American Association for the Advancement of Science.
The Bat Bot weighs only 93 grams and is shaped like a bat with a roughly one-foot wingspan. It is capable of altering its wing shape by flexing, extending, and twisting at its shoulders, elbows, wrists, and legs. Arguably, bats have the most sophisticated powered flight mechanism among animals, which includes wings that have the capability of changing shape. Their flight mechanism involves several different types of joints that interlock the bones and muscles to one another, creating a musculoskeletal system that is capable of movement in more than 40 rotational directions.
“Our work demonstrates one of the most advanced designs to date of a self-contained flapping-winged aerial robot with bat morphology that is able to perform autonomous flight,” Ramezani says.
One of the key challenges was to create wings that change shape while flapping, the way a biological bat’s do. Conventional lightweight fabrics, like nylon and Mylar, are not stretchable enough. Instead, the researchers developed a custom ultra-thin (56 microns), silicone-based membrane that simulates stretchable, thin bat wings.
Bat-inspired aerial robots have the potential to be significantly more energy efficient than current flying robots because their flexible wings amplify the motion of the robot’s actuators. When a bat—or the Bat Bot—flaps its wings, the wing membranes fill up with air and deform. At the end of the wings’ downward flapping motion, the membranes snap back to their usual shape and blast out the air, creating a huge amplification in power for the flap.
The design has potential applications for environments where more traditional quadrotor drones—which have four spinning rotors—could collide into objects or people, causing damage or injury.
Today many biofuel refineries operate for only seven months each year, turning freshly harvested crops into ethanol and biodiesel. When supplies run out, biorefineries shut down for the other five months. However, according to recent research, dual-purpose biofuel crops could produce both ethanol and biodiesel for nine months of the year—increasing profits by as much as 30%.
“Currently, sugarcane and sweet sorghum produce sugar that may be converted to ethanol,” said co-lead author Stephen Long, Gutgsell Endowed Professor of Plant Biology and Crop Sciences at the Carl R. Woese Institute for Genomic Biology at the University of Illinois. “Our goal is to alter the plants’ metabolism so that it converts this sugar in the stem to oil—raising the levels in current cultivars from 0.05% oil, not enough to convert to biodiesel, to the theoretical maximum of 20% oil. With 20% oil, the plant’s sugar stores used for ethanol production would be replaced with more valuable and energy dense oil used to produce biodiesel or jet fuel.”
A paper published in Industrial Biotechnology simulated the profitability of Plants Engineered to Replace Oil in Sugarcane and Sweet Sorghum (PETROSS) with 0%, 5%, 10%, and 20% oil. They found that growing sorghum in addition to sugarcane could keep biorefineries running for an additional two months, increasing production and revenue by 20-30%.
Today, PETROSS sugarcane produces 13% oil by dry weight, 8% of which is the kind of oil used to make biodiesel. At 20% oil, sugarcane would produce 13 times more oil—and six times more profit—per acre than soybeans.
A biorefinery plant processing PETROSS sugarcane with 20% oil would have a 24% international rate of return—a metric used to measure the profitability of potential investments—which increases to 29% when PETROSS sorghum with 20% oil is processed for an additional two months during the sugarcane offseason.
“When a sugarcane plant has to shut down, the company is still paying for capital utilization; they have spent millions of dollars on equipment that isn’t used for five months,” said co-lead author Vijay Singh, Director of the Integrated Bioprocessing Research Laboratory at Illinois. “We propose bringing in another crop, sweet sorghum, to put that equipment to use and decrease capital utilization costs.”
By decreasing capital utilization costs, the cost to produce ethanol and biodiesel drops by several cents per liter. Processing lipid-sorghum during the lipid-cane off-season increased annual biofuel production by 20 to 30%, thereby increasing total revenue without any additional investment in equipment.
The simulations in this paper accounted for the equipment required to retrofit ethanol plants to produce biodiesel. In the U.S., about 90 percent of ethanol plants are already retrofitted to produce biodiesel. According to Singh, in places like Brazil where they produce a large amount of sugarcane, it makes sense to retrofit ethanol plants. “Our study shows that it is cost effective to do it.”
In contradicting a theory that’s been the standard for over eighty years, an Illinois group led by Yang Zhang, assistant professor of Nuclear, Plasma, and Radiological Engineering and Beckman Institute for Advanced Science and Technology, has made a discovery holding major promise for the petroleum industry.
The research has revealed that in the foreseeable future products such as crude oil and gasoline could be transported across country 30 times faster, and the several minutes it takes to fill a tank of gas could be reduced to mere seconds.
Over the past year, using high flux neutron sources at the National Institute of Standards and Technology (NIST) and Oak Ridge National Laboratory (ORNL), Zhang’s group has been able to videotape the molecular movement of alkanes, the major component of petroleum and natural gas. The group has learned that the thickness of liquid alkanes can be significantly reduced, allowing for a marked increase in the substance’s rate of flow.
“Alkane is basically a chain of carbon atoms,” Zhang said. “By changing one carbon atom in the backbone of an alkane molecule, we can make it flow 30 times faster.”
The discovery of Zhang, his graduate students Ke Yang, Zhikun Cai, and Abhishek Jaiswal, and collaborators Dr. Madhusudan Tyagi at NIST and Jeffrey S. Moore, Interim Director of the Beckman Institute and HHMI Professor of Chemistry at Illinois, disproves a well-known theory that Princeton University Profs. Walter Kauzmann and Henry Eyring formed in the late 1940s. They had predicted that all alkanes have a universal viscosity near their melting points. Zhang said the theory had been cited over 3,000 times.
However, a rather distinct odd-even effect of the liquid alkane dynamics was discovered. The odd-even effect in solid alkanes is taught in almost every introductory organic chemistry textbook, i.e., the difference in the periodic packing of odd- and even-numbered alkane solids results in odd-even variation of their densities and melting points. However, the same effect was not expected in liquid alkanes because of the lack of periodic structures in liquids.
“We would have thought that no structural memory may carry over from the solids to the liquids,” Prof. Martin Gruebele, the James R. Eiszner Chair Professor in Chemistry, said, “but clearly, the cooler liquid already has the origins of the odd-even effect built into its diffusion!”
“The classical Kauzmann-Eyring theory of molecular viscous flow is over simplified,” Zhang said. “It seems some chemistry textbooks may need revisions.”
The Illinois scientists had the technological advantage of super high-speed (at the pico-second, 1 trillionth of a second) and super high-resolution (at the nano-meter, 1 billionth of a meter) “video cameras” making use of neutrons to take movies of the molecules. “A neutron ‘microscope’ is the major breakthrough in materials research and we use it to look at everything. There are things we’ve never seen before,” Zhang said.
The research, “Dynamic Odd-Even Effect in Liquid n-Alkanes near Their Melting Points,” has been published in Angewandte Chemie International Edition. The German publication is one of the top chemistry journals in the world. The reported research discovery is fundamental to understand and improve a wide spectrum of chemical processes, such as lubrication, diffusion through porous media, and heat transfer.
Zhang conducted the research after being selected in fall 2015 for an American Chemical Society Petroleum Research Fund Doctoral New Investigator Award. The first author of the paper, Ke Yang, graduated in summer 2016 and now works at the Dow Chemical Company.
Researchers from the University of Illinois at Urbana-Champaign have demonstrated doping-induced tunable wetting and adhesion of graphene, revealing new and unique opportunities for advanced coating materials and transducers.
“Our study suggests for the first time that the doping-induced modulation of the charge carrier density in graphene influences its wettability and adhesion,” explained SungWoo Nam, an assistant professor in the Department of Mechanical Science and Engineering at Illinois. “This work investigates this new doping-induced tunable wetting phenomena which is unique to graphene and potentially other 2D materials in complementary theoretical and experimental investigations.”
Graphene, being optically transparent and possessing superior electrical and mechanical properties, can revolutionize the fields of surface coatings and electrowetting displays, according to the researchers. A material’s wettability (i.e. interaction with water) is typically constant in the absence of external influence and are classified as either water-loving (hydrophilic) or water-repelling (hydrophobic; water beads up on the surface). Depending on the specific application, a choice between either hydrophobic or hydrophilic material is required. For electrowetting displays, for example, the hydrophilic characteristics of display material is enhanced with the help of a constant externally impressed electric current.
“What makes graphene special is that, unlike conventional bulk materials, it displays tunable surface wetting characteristics due to a change in its electron density, or by doping,” said Ali Ashraf, a graduate student researcher and first author of the paper, “Doping-Induced Tunable Wettability and Adhesion of Graphene,” appearing in Nano Letters. “Our collaborative research teams have discovered that while graphene behaves typically as a hydrophobic material (due to presence of strongly held air-borne contamination on its surface), its hydrophobicity can be readily changed by changing electron density.
Researchers have created a robotic mimic of a stingray that’s powered and guided by light-sensitive rat heart cells.
The work exhibits a new method for building bio-inspired robots by means of tissue engineering. Batoid fish, which include stingrays, are distinguished by their flat bodies and long, wing-like fins that extend from their heads. These fins move in energy-efficient waves that emulate from the front of the fin to the back, allowing batoids to glide gracefully through water. Inspired by this design, Sung-Jin Park et al. endeavored to build a miniature, soft tissue robot with similar qualities and efficiency. They created neutrally charged gold skeletons that mimic the stingray’s shape, which were overlaid with a thin layer of stretchy polymer.